Arbitrary function generator



g- 22, 1961 J. T. SAWYER ETAL Re. 25,032

ARBITRARY FUNCTION GENERATOR Original Filed April 29. 1957 2Sheets-Sheet 1 IN EN] 5. E S WYER E l5 ORA AtZZyS.

W WR JQ 1961 J. T. SAWYER EI'AL Re. 25,032

ARBITRARY FUNCTION GENERATOR Original Filed April 29, 1957 2Sheets-Sheet 2 INVENTORSZ JAMES F SAWYER Y JOHN KE-LLIS FLORA flat/ 5.5/

United States Patent 25,032 ARBITRARY FUNCTION GENERATOR James T. Sawyerand John 'Kellis Flora, Huntsville, Ala.,

assignors to 'Compudyne Corporation, Hatboro, Pa., a

corporation of Pennsylvania Original No. 2,835,773, dated May 20, 1958,Ser. No.

655,640, Apr. 29, 1957. Application for reissue May 17, 1960, Ser. No.30,059

7 Claims. (Cl. 338-89) Matter enclosed in heavy brackets appears in theoriginal patent hut forms no part of this reissue specification; matterprinted in italics indicates the additions made by reissue.

This invention relates to an electrical device designated as anarbitrary function generator. It has for its main Objects to providesuch a device that will be highly satisfactory for the purpose intended,simple in structure, comparatively cheap to manufacture, easy to use andkeep in working condition, and extremely durable.

Also the arbitrary function generator made according to this inventionaccomplishes the purpose of producing a voltage proportioned to theordinate of a curve drawn with special conducting ink or fluid on paperor other insulating material. The advantage of being able to produce avoltage directly from a curve drawn on paper is that this method ofpreparing a function for conversion to a voltage is very inexpensive,convenient, and quick.

Other objects and advantages will appear from the drawings anddescription.

By referring generally to the drawings, it will be observed that Fig. 1is a plan view of an arbitrary function generator made according to thepresent invention; Fig. 2 is a side elevational view of Fig. 1; Fig. 3is an end elevational view of Fig. 1; Fig. 4 is a circuit diagram of thegenerator; and Fig. 5 is a perspective view of parts of the deviceshowing the principle of operation.

Similar reference numerals refer to similar parts throughout the severalviews.

Referring to the drawings in detail it will be seen that the structureof the device comprises a rotatable metal drum- 1 which is adapted to bedriven by a suitable electric motor, a sheet of paper 2 attached aroundthe drum, a curved line of electrically conductive ink 3 on the paper, awire-wound potentiometer 4 with a resistance preferably exceeding abouttwo thousand ohms, two rollers 5 made of ordinary metal plated with aprecious metal so that the surface of the rollers will not corrode, tothus maintain good electrical contact properties. Wires 6 are connectedas shown in FIG. 5. A main base 7 supports the side members 8. The drumis mounted on a shaft 9 that is supported in bearings in the sidemembers. The drum is revolved by an electric motor 10 connected by chain11 and sprockets 12 and 13. The side members are provided with slots14in which the shaft ends 15, 16 and 17 of the potentiometer 4 androllers 5 are slidable. Springs 18, 19 and 20 are attached on studs 2-1,22 and 23 and are adapted to hold the potentiometer and rollers adjacentthe ink or fluid line on the paper on the drum. A spring type clip 24holds the end of the paper on the drum.

Any suitable conductive ink may be used, such as Du Pont #4922 silverpaste or similar, butyl acetate or other suitable solvent, Sauereisen#P-l porcelain cement, or other finely ground inorganic filler; a smallamount of plastic such as polyethylene dissolved in the butyl acetatesolvent. The ink, when thinned to the proper consistency, flows easilyand smoothly from an ordinary ruling pen, dries in about two minutes,and leaves a hard, durable line, which on the average is about inch wideand is about .001 to .002 inch high. In the present invention thestraightness tolerances of the potentiometer roller,

Re. 25,032. Reissued Aug. 22, 1961 ice is for this type application thatit excels due to the ease and rapidity with which new ink or fluidcurves can be prepared. Important features of the invention are that itis simple, convenient, and easy to operate. It also accurately producesvoltage proportional to the ordinate of almost any shape of curve thatcan be drawn including step functions. In the past devices used toaccomplish this purpose in this category have relied upon the use ofservo-positioned followers or the use of wire glued to paper or insertedin a groove in a drum with a sliding contact maintained between the wireand potentiometer. The disadvantages of the former method arecomplexity, unreliability, possibility of the follower losing the curveand the limitation on the shape of acceptable curves. The disadvantagesof the latter method are inconvenience of attaching the wire to thepaper, or drum, the rapid wear on the potentiometer, the tendency towardnoisy operation and the limitation on the shape of acceptable curves.These disadvantages are eliminated in the present invention by utilizingdirect rolling contact and an ink or fluid line which can be easilydrawn to any shape desired. It is also especially to be noted that acontact roller is located immediately to each side of the potentiometerroller, electrical continuity is required only between the potentiometerroller and either one of the contact rollers.

The various parts of the device may be made of any material suitable forthe purpose, but we prefer to use materials generally used for suchpurposes. Also the parts may be made in different sizes and capacitiesdepending on how and where to be used.

While we have shown and described the preferred embodiment of ourinvention, we do not wish to limit same to the exact and precise detailsof structure, and reserve the right to make all modifications andchanges so long as they remain within the scope of the invention and thefollowing claims.

Having described our invention we claim:

1. An arbitrary function generator of the class described comprising, amain supporting base, upward extending portions as sides attachedopposite each other on the edge of the base, a shaft, said shaftsupported by bearings in said sides, a metal drum mounted on said shaft,a sheet of paper attached removably around on the circumference face ofsaid drum, a line of electric conductive ink upon said paper, said lineof ink starting at an edge of the paper at an end of the drum andextending on the paper and curved around the drum and ending at :theother edge of the paper at the other edge of the drum, said ink being ofa quality to cause electric current to be transmitted thereby, the outerface of said ink line being slightly extended beyond the face of thepaper; a roller potentiometer mounted by its ends supported in slots insaid sides with its circumference face in contact with said ink line onsaid paper, springs attached to the ends of said roller potentiometeradapted to retain it in close contact with said ink line and paper, twocontact rollers mounted by their ends in slots in said sides, saidcont-act rollers being positioned one along and near each side of saidpotentiometer, the circumference faces of said contact rollers being incontact with said ink line and paper, springs attached to the ends ofsaid contact rollers adapted to retain them in close contact with saidink line and paper; electric transmitting wires attached to'said contactrollers; an electric motor mounted on said base and connected byvariable chains and gears driving means to said drum for revolving same;said conductive ink being adapted to complete an electric circuitbetween said roller potentiometer and said contact rollers when the drumis being revolved and the ink line surface is in contact with saidrollers.

2. An arbitrary function generator of the class described oomprising, amain supporting base, upward extending sides attached opposite eachother on opposite edges of the base, a shaft, said shaft supported bybearings in said sides, a chart drum mounted on said shaft, graph paperattached removably around on the entire circumference face of the drum,a line of electric conduotive ink upon said paper, said line of inkstarting at one edge of the paper and extending as a curve once aroundthe drum on the paper and ending at the other edge of the paper, theouter face of said ink line being slightly extended beyond the face ofthe paper; a roller potentiometer mounted by its ends, said ends beingsupported in slots in said sides on the base with the circumference faceof the potentiometer in contact with said ink line on said paper,springs attached to the ends of the roller potentiometer adapted toretain it in close contact with said ink line and paper, two contactrollers mounted by their ends in slots in said sides, said contactrollers being disposed one along and near each side of saidpotentiometer, the circumference faces of said contact rollers being incontact with said ink line and paper, springs attached to the ends ofsaid contact rollers for holding them in close contact with said inkline and paper; a plurality of electric transmitting wires removablyattached to said contact rollers; an electric motor mounted on said baseand connected by variable chains and gears as driv ing means to saiddrum shaft for revolving the drum at different speeds, said conductiveink being adapted to complete an electric circuit between said rollerpotentiometer and said contact rollers when the drum is being revolvedand the ink line surface is in contact with said rollers.

3. An arbitrary function generator of the class described having meansfor obtaining a voltage proportionate to the ordinate of a drawn curve,said means cornprising, a main supporting base, upward extending sidesattached opposite each other on opposite edges of the base, a shaft andbearings therefor, said shaft supported by the bearings in said sides, adrum designated as a chart drum, said drum mounted on a shaft andbearings therefor, said shaft bearings mounted in said sides, a sheet ofgraph paper attached removably around on the entire circumference faceof the drum, a line of electric conductive fluid upon said paper, saidline of fluid starting at one edge of the paper at an end of the drumand extending in curve shape once around the drum and on the paper andending at the other edge of the paper at the opposite end of the drum,the outer face of said fluid line being slightly extended beyond theface of the paper; a roller type potentiometer mounted by its ends, saidends being supported in slots in said sides on the base with thecircumference face of the potentiometer in contact with said fluid lineon the paper, springs attached to the ends of the potentiometer adaptedto retain it by tension of the springs in close contact with said fluidline and paper; two contact rollers with shaft ends, slots in saidsides, said contact rollers mounted by the ends of their shafts in saidslots, said rollers being positioned one along and near each side ofsaid potentiometer, the circumference faces of said contact rollersbeing in contact with said fluid line and paper, springs attached to theshaft ends of said contact rollers, said springs by tension thereofadapted to retain said contact rollers in close contact with said fluidline and paper; a plurality of electric current transmitting wiresremovably attached to said contact rollers; an electric motor mounted onsaid base and connected by variable chains and gears as driving means tosaid drum shaft for revolving the drum at ditferent speeds; saidelectric conductive line on the paper being adapted to complete anelectric circuit between said roller potentiometer and said contactrollers at any place along the fluid curved line when the drum is. beingrevolved and contacts are maintained between the faces of the three saidrollers and the surface of the fluid line.

4. An arbitrary function generator of the class described comprising asupporting frame, a sheet support rotatably supported on the frameproviding a surface of rotation about the axis of rotation and adaptedto removably support an insulating sheet against said surface ofrotation, a potentiometer resistance element, at least one conductivecontact member, said potentiometer resistance element and said conductive contact member each being supported on the supporting frame inopposition to surfaces on the sheet support so that they are urgedtoward the sheet support and into contact with any conductive line onany insulating sheet which may be supported on said surfaces of thesheet support, whereby said conductive line is adapted to complete anelectric circuit between said potentiometer resistance element and saidconductive contact member, the variable generated by the arbitraryfunction generator being primarily the resistance of the potentiometerbetween the conductive line and one end of the potientometer resistanceelement which may vary in accordance with any arbitrarily selectedfunction as the sheet support is rotated.

5. The arbitrary function generator of claim 4 in which the sheetsupport is a right circular cylindrical drum supported on the frame torotate about its major axis and the potentiometer resistance element andat least one canductive contact member are generally parallel elementsurged into contact with the drum or a conductive line on an insulatingsheet supported thereon.

6. The arbitrary function generator of claim 5 in which there are twoconductive contazct members each of which is a roller with its axis ofrotation parallel to that of the sheet support drum and in which thecontact rollers are positioned on each side of the potentiometerresistance element and close spaced theretov 7. An arbitrary functiongenerator of the class described comprising a supporting frame, a rightcircular cylindrical drum adapted to removably support a flexible sheet,a flexible sheet mounted on the drum to conform to its cylindricalsurface and having a conductive line on its outer surface extendingabove the plane of the paper, a potentiometer resistance elementsupported on the frame parallel to the axis of the drum and urged towardthe drum and into electrical contact with the conductive line on thesheet, at least one conductive roller rotatcbly supported on the frameand resiliently urged toward the drum and into electrical contact withthe conductive line on the sheet, electrical connections on at least oneconductive roller and on one end of the' potentiometer resistanceelement so that in a circuit between the terminals the conductive lineon the sheet completes a circuit between the roller and some point onthe potentiometer resistance element and the resistance varies inaccordance with the length of the potentiometer resistance between thecontact point and the terminal.

References Cited in the file of this patent UNITED STATES PATENTS2,554,811 Brornberg et al May 29, 1951 2,662,955 Erkelens Dec. 15, 19532,761,102. Brown Aug. 28, 1956 2,820,871 Smith Jan. 21, 1958 FOREIGNPATENTS 694,260 Germany July 4, 1940

